Synthesis of Ultralarge Molecular Weight Bottlebrush Polymers Using Grubbs' Catalysts

Abstract

This paper describes two methods to synthesize bottlebrush polymers with molecular weights from 1 million to over 60 million g mol-1 using Grubbs' first and second generation catalysts. In the first method, macromonomers of poly(l-lactide) were synthesized using tin(II) 2-ethylhexanoate and terminated on one end with a norbornyl group. Grubbs' first generation catalyst polymerized macromonomers with one poly(l-lactide) chain per norbornene, and Grubbs' second generation catalyst polymerized macromonomers with two poly(l-lactide) chains per norbornene. The predicted and measured molecular weights closely matched each other, and the polydispersities of the bottlebrush polymers were between 1.05 and 1.39. These examples are the first where Grubbs' second generation catalyst can be considered living for ROMP. In the second method, the backbone was polymerized first, and polylactide arms with molecular weights from 15 000 to 50 000 g mol-1 were polymerized from the backbone. Polymers that were shaped as spheres or rigid rods were synthesized. The polymers were analyzed by GPC, MALLS, QELS, and 1H NMR.